Applicability of Johnson-Mehl-Avrami model to crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy

The applicability of Johnson-Mehl-Avrami(JMA) model to the crystallization kinetics of Zr60Al15Ni25 bulk amorphous alloy is investigated by differential scanning calorimetry(DSC) under isochronal and isothermal conditions. A criterion xm, at which a defined function z(x) exhibits the maximum value, is introduced to check the validity of JMA model to the kinetics analysis. The value of xm has a constant of 0.632 for JMA model. It is found that the values of xm at different isothermal annealing temperatures (743, 748, 753 and 758 K) are almost near 0.632, which indicates that the isothermal crystallization kinetics can be modeled by JMA equation. However, the values of xm at different heating rates (10, 20, 30 and 40 K/min) are about 0.52, implying that JMA model is not valid to the isochronal crystallization kinetics. The reason why the JMA model is not valid to the isochronal crystallization kinetics is discussed.